Patent GB-1265581-A (GB)
IPC: G06F15/02
Filed: 1969-02-17
Abstract: 1,265,581. Calculators. BELL PUNCH CO. Ltd. 28 May, 1969 [17 Feb., 1969], No. 8576/69. Heading G4A. In a calculating machine having two shift registers each with a plurality of digit stages into each of which a digit pulse count representative of a digit can be entered, operation of a function key switch transfers a digit from the first register to the second, with or without clearing of the digit from the first register according to the position of a constant key switch. The first (input) register and second (accumulator) register each comprise four shift registers in parallel recirculating via respective stages of a buffer counter and each provide storage for 13 binary-coded-decimal digits. Each buffer counter can be incremented, either by a train of n pulses representing a digit of value n from a digit keyboard to enter the digit, or to transfer a store digit to another buffer counter by also incrementing the latter under control of a carry-out bi-stable of the source buffer counter, the buffer counter in the input register and that in the accumulator register having two carry-out bi-stables each. Digits in either the input register or the accumulator register can be displayed, as can the decimal point position in the accumulator register as indicated by a decimal point counter, by transferring each digit and the count in turn to a buffer counter which supplies it in binary coded form to a staticizer which controls one of a row of number tubes or a set of decimal-point indicating neon tubes, the number tubes and the set of neon tubes being selected in turn for this purpose by a clock-driven timer circuit (a decoded Johnson counter). By changing the number of shift pulses, the input or accumulator register can be shifted in either direction relative to the timer circuit (and thus the display), a slip counter keeping a record of the extent of the relative shift. A function control counter is controlled by a function keyboard comprising add, subtract, multiply, divide, decimal point, enter and constant keys. The constant key in the released position causes digits entered from the digit keyboard to enter the input register but in the actuated (or latched-down) position causes the contents of the input register to be retained and any digits entered to go into the accumulator register. For addition, the input register decimal-point position is subtracted from the accumulator register decimal-point position in the decimal-point counter, the decimal points are aligned by relative shift of the registers, and the input register contents are added into the accumulator register using their respective buffer counters for transfer as described above. Then each digit in the accumulator register is transferred to the buffer counter used for the display, the digit position in each register is cleared, and the buffer counter contents are copied into both registers. If the enter key is pressed immediately after switch-on or entry of a number, the accumulator register is cleared then addition as above takes place. If it is pressed after a function key the cleared input register is added into the accumulator register and the result copied into both registers. Subtraction is by complementary addition. In the copying referred to above, if the result to be copied is negative, its complement is copied instead. If the enter key is pressed after an arithmetical operation has been completed, the input register is cleared and the accumulator register is not cleared. Momentarily depressing and then releasing the constant key can be done to clear an incorrectly-entered number from the input register. With the constant'key in the latched down position a number from the keyboard is entered into the accumulator register rather than the input register, as stated above, and by releasing this key, before relatching it, an incorrectly-entered number is cleared from the accumulator register. If the constant key is latched down, the number in the input register can be used in addition, subtraction, multiplication or division, but the result is not copied into the input register.